In the field of industrial packaging it is frequent to use containers with envelopes of flexible material, essentially of tubular shape, which, after they have been filled by means of a filling operation, are closed at the two ends by means of a tying or a clipping operation.
The filling operation in particular is carried out in the packaging of alimentary products and above all in the packaging of ground products based on meat to obtain the so called filled material called "insaccati", in which the envelope is constituted by a tube from the intestine of an animal referred to hereinbelow as "budello", which is filled with the paste of ground meat, for instance to prepare salami and sausages and similar material.
According to the present state of the art, the filling operation of ground meat is carried out substantially with packaging machines in which the operator inserts in the conduit being used for feeding the product to be filled in the open end of the tube containing budello while the opposite end of the same is preliminarily closed by means of a knot with a string or by a neck with a clip. After the predetermined quantity of the product is deposited in the interior of the budello the operator takes care of closing manually the end thus providing the filled product.
A drawback of the above process, both when the filling occurs manually as described hereinabove and also when the filling is carried out by means of automatic machines, resides in the fact that the closure of the container is not perfect at the end of the operation of introduction of the product in the budello and the result is an irregular clipping operation. In fact the product to be filled contains always in its interior small particles filiforms, which are constituted in the case of a meat paste, by cartilages, small pieces of nerve tissue and similar material, a lint, usually called "sfilacci". During the closing operation of the container by a clipping operation, that is by forming the neck in the terminal part of the budello, these filiform products may remain trapped in the clipping zone with the result that they protrude in part from the product which has been filled and it is not possible to achieve a regular and complete closure of the metallic strip with the result that eventually the budello may break in the clipping zone.